1. Field of the Invention
This invention relates to an optical device provided with a tremble correcting function which corrects a tremble of a focused image.
2. Description of the Related Art
Conventionally, in the field of optical devices, for example binoculars, there is a type which is provided with a tremble preventing function. The tremble preventing function is a function which corrects a focused image tremble caused by a hand tremble and so on.
For example, in binoculars, the tremble preventing function is carried out by a tremble detector, a pair of correcting optical systems, and a driving mechanism. The tremble detector detects a tremble of left and right telephoto optical systems. The driving mechanism drives the pair of correcting optical systems in two directions on a plane which is perpendicular to the optical axes of the correcting optical systems. The correcting optical systems are positioned between the objective optical systems and the inversion optical systems such that one of the correcting optical systems is included in the right telephoto optical system and the other of the correcting optical systems is included in the left telephoto optical system.
When the binoculars are shaken by a hand tremble or such like, the tremble of the optical axes of the telephoto optical systems is detected by the tremble detector. The correcting optical systems are driven by the driving mechanism in the two directions crossing at right angles on the plane perpendicular to the optical axes of the correcting optical systems such that the tremble of the optical axes is canceled. Consequently, the tremble of the image obtained by the telephoto optical systems is prevented.
As the driving mechanism, a stepping motor, for example, is utilized. In the stepping motor, a rotational movement of a rotor is converted to a linear movement in a thrust direction of a shaft, by a screw feeder mechanism. A holding member of the pair of correcting optical systems is driven in accordance with the movement of the shaft in the thrust direction. Accordingly, a driving direction and a driving amount of the holding frame are decided by controlling an electric current which flows through a coil of a stator of the stepping motor.
As described above, the screw feeder mechanism is utilized for converting the rotational movement of the rotor to the linear movement of the shaft. Accordingly, in a situation where the supply of electric power to the stepping motor is stopped, it is extremely difficult to supply sufficient external power in the thrust direction of the shaft so that the torque required to rotate the rotor is generated.
In other words, when the supply of electric power to the stepping motor is stopped, the rotor is stopped and the shaft is fixed at a position in the thrust direction, at which the shaft is stopped at that time. Consequently, the correcting optical systems are fixed at a position at which they are stopped when the electric power supply was stopped.
The above-mentioned tremble preventing function is not always working while the binoculars are being used. For example, there is a tremble preventing button, which is placed at a predetermined position on the outer surface of a case of the binoculars. By manipulating the tremble preventing button, the start and stop of the tremble preventing function are controlled. Namely, the tremble preventing function is optionally carried out in accordance with the situation. Further, the tremble preventing function is independent from other functions, for example, the focusing function and the interpupillary adjustment function. Accordingly, an object can be viewed by the binoculars without carrying out the tremble preventing function.
Generally, users carry the binoculars to a place to be observed. Accordingly, in binoculars provided with the tremble preventing function, a battery is utilized as an electric power supply for the stepping motor. Because, the battery is very portable, it does not reduce the portability of the binoculars.
However, the amount of electric power supplied by the battery is limited. Accordingly, the supply from the battery may be suddenly stopped, while the tremble preventing function is being carried out. If the supply is suddenly stopped, the correcting optical systems may be fixed in a state where the optical axes of the correcting optical systems do not coincide with the optical axes of the other optical systems of the telephoto optical systems.
As described above, it is possible to observe the object with the binoculars even if the tremble preventing function does not work. Accordingly, if the correcting optical systems is fixed in the above-mentioned state, that is, the optical systems do not coincide, there is a problem that an actual object image viewed through the telephoto optical systems does not coincide with a theoretical (desired) object image that lies on the optical axis of the lens barrels of the binoculars, making the user feel slight physical discomfort.
Therefore, an object of the present invention is to make sure that an actual object image coincides with the theoretical (desired) object image that lies on an optical axis of a lens barrel, in an optical device provided with a tremble preventing function.
In accordance with an aspect of the present invention, there is provided an optical device, provided with a tremble preventing function, comprises: a tremble detector that detects an amount of an optical device tremble; a correcting optical system, included in an imaging optical system of the optical device, that corrects a tremble of a focused image due to the optical device tremble; a driving system that drives the correcting optical system in two directions on a plane perpendicular to an optical axis of the correcting optical system, and continues to maintain a position of the correcting optical system when a power supply to the optical device is stopped; a controller that controls the driving system such that the optical device tremble amount is canceled; a power battery that supplies electric power to the driving system; and a voltage level detector that detects an output voltage level of the power battery. When the output voltage level detected by the voltage level detector is below a predetermined threshold, the correcting optical system is driven to a standard position such that the optical axis of the correcting optical system coincides with an optical axis of other optical systems included in the imaging optical system.
Preferably, the value of the threshold is set such that the remaining amount of electric power in the power battery is enough for the driving system to drive the correcting optical system from a moving limit position to the standard position. The moving limit position is defined by a holding member of the correcting optical system and is the furthest position from the standard position.
Preferably, the optical device further comprises a memory in which the predetermined threshold is stored.
For example, the memory is an EEPROM.
In accordance with another aspect of the present invention, there is provided an optical device comprising:
a correcting optical system, included in an imaging optical system of the optical device, for correcting a tremble of a focused image due to an optical device tremble; and
a tremble preventing function which corrects the focused image tremble by driving the correcting optical system such that the optical device tremble can be cancelled. When the tremble preventing function is not carried out, the correcting optical system is maintained at all times at a position at which an optical axis of the correcting optical system coincides with an optical axis of other optical systems of the imaging optical system of the optical device.
As described above, according to the present invention, when the output voltage level of the battery becomes lower than the predetermined threshold, the correcting optical system is driven to the standard position. Accordingly, even if the output voltage level falls while the tremble prevention function is working, the position of the correcting optical system is changed to a state where the optical axis of the correcting optical system coincides with the optical axes of the other optical systems of the imaging optical system.
Further, the value of the predetermined threshold is set such that the correcting optical system can be driven from the moving limit position to the standard position. Accordingly, the correcting optical system is reliably driven to the standard position.